Networks that primarily utilize data link layer devices are often referred to as layer two (L2) networks. A data link layer device is a device that operates within the second layer of the Open Systems Interconnection (OSI) reference model, i.e., the data link layer. One example of a data link layer device is a customer premises equipment (CPE) device, such as a switch, modem, Ethernet card, or wireless access point. Traditional L2 networks include Ethernet networks, Asynchronous Transfer Mode (ATM) networks, Frame Relay networks, networks using High Level Data Link Control (HDLC), Point-to-Point (PPP) connections, PPP sessions from Layer 2 Tunneling Protocol (L2TP) tunnels, and Virtual Local Area Networks (VLANs).
In some instances, a layer three (L3) network is used as an intermediate transport network between two or more L2 networks in order to allow communication between the L2 networks. In this type of configuration, the L3 network transparently transports L2 communication between the L2 networks, thereby allowing the L2 networks to share an L2 service. Common protocols for transporting the L2 service through the intermediate L3 network are label switching protocols, such as Multi-protocol Label Switching (MPLS) protocols like Resource Reservation Protocol (RSVP) and the Label Distribution Protocol (LDP). In accordance with MPLS, a source device, such as a router connected to one of the L2 networks, can request a path through the intermediate network. This path, referred to as a Label Switched Path (LSP), defines one or more distinct, dedicated, and guaranteed paths through the network to carry MPLS packets from the source to the destination. The MPLS packets encapsulate the L2 communications, thereby effectively shielding the L3 network from the transported L2 information.
One example of an L2 service is the Virtual Private LAN Service (VPLS), also referred to as Point-to-multipoint (P2MP) L2 VPNs. In general, VPLS allows two or more remote customer networks to be extended through the intermediate network as if the intermediate network does not exist. In particular, L2 communications, such as Ethernet packets, are transported between customer networks via the intermediate network. In a typical configuration, VPLS-enabled routers that are associated with the customer networks define LSPs within the intermediate network to carry encapsulated L2 communications as if these customer networks were directly attached to the same LAN. To properly communicate via these LSPs, each of these VPLS-enabled routers store L2 information, such as Media Access Control (MAC) addresses, as well as VPLS information, such as local and remote VPLS site information. In this manner, these VPLS-enable routers provide transparent L2 connectivity across the intermediate network and simulate a direct LAN.
While a VPLS may provide transparent L2 connectivity across a single intermediate network, establishing L2 connectivity via VPLS across one or more intermediate networks becomes increasingly difficult, especially when the intermediate networks are provided by different service providers. In particular, the intermediate networks may not support VPLS, and the service providers associated with the intermediate networks may be unwilling to do so due to the increased overhead and cost associated with VPLS. For example, the service providers may be unwilling to incur the increased overhead and cost associated with storing and managing the L2 state information associated with the VPLS service.